How tight junctions might prevent small charged solutes from entering the brain (across the blood-brain barrier) is made clear by our new model of tight junction structure based on a lipidic backbone. Tight junctions in invertebrates also appear to have lipid backbones though our most recent observations suggest that periodic structures, presumably proteins are intercalated into these backbones. This new work has been submitted for publication, and publications describing completed studies on the three-dimensional organization of the vesicular system in capillaries are appearing this year. Otherwise this project is in abeyance.